Deep Arctic Waters Still Flowed During Last Ice Age

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Even during the deep freeze of the last ice age, the waters of
the deep Arctic Ocean churned below the frozen ice cap, new
research finds.

Scientists thought that these waters slowed or even stopped
during this time, but analysis of sediment from the bottom of the
ocean shows that these waters have been churning for the past
35,000 years under wildly different climates.

The deep basins of the Arctic are
flushed by water that is created as sea ice forms at the ocean's
surface; the water that freezes into ice leaves water enriched in
salt behind, which sinks to the ocean bottom. The waters of the
deep Arctic are a critical branch of the global
ocean circulation, which moves heat around the planet along
with atmospheric circulation. In the modern ocean, these waters
flow into the North Atlantic, where they help bring oxygen and
salt to the rest of the world's oceans, according to a release on
the research from Columbia University's Lamont-Doherty Earth
Observatory. [ 10
Things You Need to Know About Arctic Sea Ice ]

Researchers from Lamont-Doherty and the Woods Hole Oceanographic
Institution in Massachusetts investigated the past flow of the
deep Arctic waters by examining the amounts of a product of
radioactive decay in the sediments buried on the ocean floor.
(The sediments came from cores drilled from the ocean floor
during a 1994 research expedition.) Rivers wash sediment into the
oceans; this sediment contains uranium, which decays into thorium
and protactinium. These two elements attach to particles in the
water, which fall to the ocean floor. The amount of the elements
in the buried sediments can tell researchers whether the
deep water was flowing fast enough to flush the sediments
out.

The study, detailed in yesterday's (May 30) issue of the journal
Nature, found that there was less protactinium than would be
expected if the deep water flow stagnated.

"The Arctic Ocean must have been flushed at approximately the
same rate it is today regardless of how different things were at
the surface," said study co-author Jerry McManus of
Lamont-Doherty.

The study results suggest that sea ice was being formed at the
surface and then melting seasonally as it does today.

"There must have been significant melt-back of sea ice each
summer even at the height of the last ice age to have sea ice
formation on the shelves each year. This will be a surprise to
many Arctic researchers who believe deep water formation shuts
down during glaciations," Robert Newton, a Lamont-Doherty
oceanographer who wasn't involved in the study, said in a
statement.

In the future, the researchers hope to find where the sediment
with the protactinium was flushed to.

"It's somewhere," McManus said in the release. "All the
protactinium in the ocean is buried in ocean sediments. If it's
not buried in one place, it's buried in another. Our evidence
suggests it's leaving the Arctic but we think it's unlikely to
get very far before being removed."